A subject of the present invention is a safety binding for a ski boot, of which the sole has a curb comprising a binding body of which a horizontal part for the boot to rest on vertically and extending under the boot, contains an axially moving element urged by an elastic means, the body carrying a sole clamp for holding the boot by its curb, this sole clamp being mounted to pivot about at least one at least approximately vertical axle and pivoting through a limited angle in a vertical plane about a real or imaginary axis located in the region where the boot is held by the sole clamp, this sole clamp being equipped with two descending arms rigidly connected to the sole clamp and the ends of which bear against said moving element.
The invention is as applicable to a front stop as it is to a heel piece. The term xe2x80x9csole clampxe2x80x9d is to be understood as meaning a part of the binding which comes onto the curb of the boot via at least one face. All indications regarding direction are given relative to the tipper face of a horizontally positioned ski.
Such a binding is known, in the form of a stop, from patent CH 686 707. This binding has the advantage that just one spring can be used to control both the pivoting of the sole clamp about a vertical axle in the event of a fall and the tilting of the sole clamp in a vertical plane, whether this be in order to maintain a certain vertical pressure on the curb of the boot and to ensure that the height of the sole clamp elastically follows the variations in height that are encountered in standardized curbs or which are due to the presence of a wedge of snow on the binding or under the boot or alternatively in order to make the boot release more readily, particularly in the event of a fall forward. This possibility of tilting allows far better control of the release of the boot in a backward fall. Furthermore, arranging the spring and the piston under the surface on which the boot rests on the binding makes it possible to obtain a good relationship between the resistive torques exerted on the boot in the horizontal plane and in the vertical plane. More specifically, the active lever arms are of the same order of magnitude.
In a binding stop it is of prime importance for the sole clamp to have a good ability to return to its initial position. In particular, it is essential that in the event of a series of lateral knocks against the boot, as often occurs, especially in competition, this series of knocks should not result in a summation of small shifts of the sole clamp liable to give rise to inadvertent release of the binding but in any case resulting in poor alignment of the boot relative to the axis of the ski as a result of incomplete return of the stop to its initial position, such a defect causing a fall through lack of control of the ski. It is therefore essential that after each of the lateral knocks, the sole clamp should return to its initial position and bring the boot back to the correct position. From this point of view, the binding described in patent CH 686 707 is not satisfactory. This is because if FIG. 2 of that document is studied, it can be seen that the thrust exerted by the sole clamp on the piston creates a significant torque on the piston in a horizontal plane, this torque causing reactive lateral pressures resulting in friction forces that oppose the sliding of the piston. Now, it is known that in a safety binding, control over friction is essential if you want the binding to release consistently for given loads.
The present invention sets out precisely to overcome the defects of the aforementioned stop.
The binding according to the invention is characterized in that the sole clamp is split into two independent sole clamps each mounted to pivot about its own at least approximately vertical axle, these sole clamps constituting two levers of the first kind having two divergent lever arms intended to retain the boot laterally and two converging arms at least approximately perpendicular to the longitudinal axis of the binding and bearing respectively against the end of the moving element via a descending arm at two closely spaced points.
As the two points at which the descending arms of the sole clamp bear are closely spaced, they are also close to the axis of the moving element. They will even advantageously be as close to this axis as possible. The torque exerted on the moving element by the sole clamp is thus very small, which means that the friction forces caused by this torque are insignificant.
Furthermore, the friction of the sole clamps on the curb of the boot are less than in a binding with a single sole clamp.
Furthermore, the fact of having two independent sole clamps encourages the sole clamps to recenter themselves and encourages escape from the binding in the event of a fall, as has already been explained in document EP 0 295 372. Front stops comprising two sole clamps are also known, particularly from document DE 27 56 995, EP 0 241 360, FR 2 464 727 or, more recently, document FR 2 758 732. In the bindings described in those documents, the spring is located at the front of the sole clamps, at the height thereof and acts on a tie rod to one end of which the arms of the sole clamps are attached. The kinematics of these stops is therefore very different than that of the binding according to the invention.
The moving element advantageously consists of a piston.
In order to have a harmonious relationship between the resistive torques of lateral retention and of tilting in a vertical plane, the distance between the imaginary axis of rotation of the sole clamps in a vertical plane and the end of points at which the descending arms bear on the piston is advantageously approximately equal to the length of the diverging lever arms of the arms of the sole clamps.
The limited tilting of the sole clamps in a vertical plane can be achieved in various ways.
In one embodiment, the pivot axles of the sole clamps about as approximately vertical axis have two axial stops retaining the sole clamps vertically and the sole clamps have, between these stops, forward angular clearance allowing the sole clamps to tilt to a limited extent.
In another embodiment, the pivot axles of the sole clamps about an approximately vertical axis are connected without clearance to the sole clamps and are connected together rigidly at their upper part by a horizontal part so as to form a single. U-shaped component mounted to pivot on the body, between two stops, about its horizontal part. The stops advantageously consist of the ends of two slots formed in the binding body and through which the pivot axles pass.
The branches of the U-shaped component advantageously diverge slightly so that the pivot axles are inclined slightly so that the path of the sole clamps, as they open, is slightly upward, which encourages the boot to escape because the sole clamp thus moves vertically away from the curb of the boot.
The amplitude of the tilting of the sole clamps in a vertical plane can be increased in order to release the boot in the event of a backward fall in the case of a front stop or to release the boot in a forward fall in the case of a heel piece.
In the case of a stop, as with the binding according to patent CH 686 807, the binding body of the stop may be articulated in a stirrup to produce a cross-country binding.
The appended drawing depicts, by way of example, a number of embodiments of the binding according to the invention.